1. Field of the Invention
This invention relates to an information recording medium and information recording/reproducing method and, more particularly, to an information recording medium and information recording/reproducing method which reduces a track pitch between information recording tracks in a recording medium, and increases the information recording density, and further enables information such as a servo-burst signal for tracking control to be easily recorded.
2. Description of Related Art
In a computer system a backup operation, i.e., copying of stored information into another recording medium, is performed periodically, so as to avoid losing information due to an accident in a storage device such as a hard disk or natural "computer disasters". As a backup recording medium or an intermediate medium to transport the information to another computer, an information recording medium such as a magnetic tape is widely used.
One known representative recording device used for this purpose is a tape streamer. The tape streamer includes, for example, a 1/4 inch magnetic tape cartridge having a number of information recording tracks provided in parallel to a tape-running direction A magnetic head provided opposing to the recording medium is moved in a direction orthogonal to the tape-running direction, so as to be positioned above a predetermined track and then performs the recording/reproducing information operation.
Recently, with an increase of information amount and downsizing of information recording media, the present inventors identified that there is an increasing need for improvement in recording line density and track density in tape streamers. However, the conventional streamer moves the magnetic head by open-loop control using a stepping motor, and lacks a function for correcting errors due to meandering of a tape and the like. For this reason, the reduction of track pitch for increasing the track density is limited.
To solve this problem, a servo system has been proposed. This control system records a tracking-control signal (servo signal) on a recording medium and causes a recording/reproducing head to follow the center of each track by using the signal. More specifically, as a servo method, the position of a recording/reproducing head is controlled by reading a pattern of a servo signal recorded in the central portion of an information recording medium and detecting tracking errors (i.e., positional shifts).
FIG. 7 shows an example of the conventional information recording medium used in the servo method. This example uses a head having a plurality of recording/reproducing gaps 114. A dedicated track 111 for servo signals, comprising servo-burst-signal recording sections 112 and servo-burst-signal non-recording sections 113, is provided on the medium. During reproduction of data on the dedicated track 111 by one of the plurality of gaps 114, if the head position is controlled such that a ratio between a signal intensity in a portion including the non-recording section 113 and that in a portion not including the non-recording section becomes 1:2, the position of a data reproduction gap is at the center of the track.
FIG. 8 is another example of a conventional information recording medium used in another servo method. In this example, information recording tracks 221 and servo-burst tracks 222 are alternatively arranged. Each servo-burst track 222 includes an optical servo-burst-signal recording section 223 and a servo-burst-signal non-recording section 224. The signal recording section 223 is irradiated with a beam, and an optical head 226 detects a reflectance of the signal recording section 223. The position of an information recording/reproducing head 225, located with a predetermined interval from the optical head 226, is controlled by controlling the position of the optical head 226 such that the detected reflectance is within a predetermined range.
FIG. 9 is another example of a conventional information recording medium used in the so-called sample-hold servo method. In this servo method, information recording tracks 331 are divided into a plurality of blocks, and a servo-burst section 332 is provided between the blocks. The servo-burst section 332 includes a plurality of pairs of servo ID sections 335 and servo-burst-signal recording sections 333, arrayed in parallel. In each array of the servo-burst section 332, the interval between the servo ID section 335 and the respective servo-burst-signal recording section 333 is staggered so as to be different from a neighboring recording section in an adjacent array. A center of each array of the servo-burst section 332 is shifted from the center of a data track in a widthwise direction of the servo-burst section 332 so that a head 334 performs reproduction of information from normally two servo-burst-signal recording sections 333. The positional deviation of the head 334 is detected by the difference between outputs from the two servo-burst-signal recording sections 333 reproduced by the head 334; thus, the head position is controlled.
However, in the servo methods applied to the conventional information recording media as shown in FIGS. 7 and 8, as dedicated servo tracks for tracking are provided continuously in a running direction of the recording-medium and in parallel to data tracks, increasing information recording capacity is limited because of the space occupied by the dedicated servo tracks. Further, in the method as shown in FIG. 9, as the positional deviation of the head 334 is detected from the output difference of servo signals reproduced from two adjacent servo-burst-signal recording sections 333, and the head position is controlled using the deviation, a plurality of servo-burst-signal recording sections are required. Accordingly increasing information recording capacity is also limited. Further, according to this method, because the servo-burst-signal recording section 333 must be provided with respect to each information recording track, time is consumed to write these signals. Additionally, the cost for implementing this method is higher than desired.